printing/pretty: Do not compute parenthesization twice

sympy/printing/pretty/pretty.py

@@ -223,7 +223,7 @@ def _print_Relational(self, e):
 
         l = self._print(e.lhs)
         r = self._print(e.rhs)
-        pform = prettyForm(*stringPict.next(l, op, r))
+        pform = prettyForm(*stringPict.next(l, op, r), binding=prettyForm.OPEN)
         return pform
 
     def _print_Not(self, e):
@@ -1873,25 +1873,9 @@ def _print_Mul(self, product):
             else:
                 a.append(item)
 
-        from sympy import Integral, Piecewise, Product, Sum
-
-        # Convert to pretty forms. Add parens to Add instances if there
-        # is more than one term in the numer/denom
-        for i in range(0, len(a)):
-            if (a[i].is_Add and len(a) > 1) or (i != len(a) - 1 and
-                    isinstance(a[i], (Integral, Piecewise, Product, Sum))):
-                a[i] = prettyForm(*self._print(a[i]).parens())
-            elif a[i].is_Relational:
-                a[i] = prettyForm(*self._print(a[i]).parens())
-            else:
-                a[i] = self._print(a[i])
-
-        for i in range(0, len(b)):
-            if (b[i].is_Add and len(b) > 1) or (i != len(b) - 1 and
-                    isinstance(b[i], (Integral, Piecewise, Product, Sum))):
-                b[i] = prettyForm(*self._print(b[i]).parens())
-            else:
-                b[i] = self._print(b[i])
+        # Convert to pretty forms. Parentheses are added by `__mul__`.
+        a = [self._print(ai) for ai in a]
+        b = [self._print(bi) for bi in b]
 
         # Construct a pretty form
         if len(b) == 0:

sympy/printing/pretty/stringpict.py

@@ -439,18 +439,21 @@ def __mul__(self, *others):
         }
 
         if len(others) == 0:
-            return self # We aren't actually multiplying... So nothing to do here.
-        args = self
-        if args.binding > prettyForm.MUL:
-            arg = stringPict(*args.parens())
-        result = [args]
+            return self  # We aren't actually multiplying... So nothing to do here.
+
+        # add parens on args that need them
+        arg = self
+        if arg.binding > prettyForm.MUL and arg.binding != prettyForm.NEG:
+            arg = stringPict(*arg.parens())
+        result = [arg]
         for arg in others:
             if arg.picture[0] not in quantity.values():
                 result.append(xsym('*'))
             #add parentheses for weak binders
-            if arg.binding > prettyForm.MUL:
+            if arg.binding > prettyForm.MUL and arg.binding != prettyForm.NEG:
                 arg = stringPict(*arg.parens())
             result.append(arg)
+
         len_res = len(result)
         for i in range(len_res):
             if i < len_res - 1 and result[i] == '-1' and result[i + 1] == xsym('*'):

sympy/printing/pretty/tests/test_pretty.py

@@ -950,6 +950,8 @@ def test_negative_fractions():
 """
     assert pretty(expr) == ascii_str
     assert upretty(expr) == ucode_str
+
+def test_Mul():
     expr = Mul(0, 1, evaluate=False)
     assert pretty(expr) == "0*1"
     assert upretty(expr) == "0⋅1"
@@ -975,8 +977,8 @@ def test_negative_fractions():
     assert pretty(expr) == "0 + 0 + 1"
     assert upretty(expr) == "0 + 0 + 1"
     expr = Mul(1, -1, evaluate=False)
-    assert pretty(expr) == "1*(-1)"
-    assert upretty(expr) == "1⋅(-1)"
+    assert pretty(expr) == "1*-1"
+    assert upretty(expr) == "1⋅-1"
     expr = Mul(1.0, x, evaluate=False)
     assert pretty(expr) == "1.0*x"
     assert upretty(expr) == "1.0⋅x"
@@ -995,6 +997,30 @@ def test_negative_fractions():
     expr = Mul(Rational(2, 3), Rational(5, 7), evaluate=False)
     assert pretty(expr) == "2/3*5/7"
     assert upretty(expr) == "2/3⋅5/7"
+    expr = Mul(x + y, Rational(1, 2), evaluate=False)
+    assert pretty(expr) == "(x + y)*1/2"
+    assert upretty(expr) == "(x + y)⋅1/2"
+    expr = Mul(Rational(1, 2), x + y, evaluate=False)
+    assert pretty(expr) == "x + y\n-----\n  2  "
+    assert upretty(expr) == "x + y\n─────\n  2  "
+    expr = Mul(S.One, x + y, evaluate=False)
+    assert pretty(expr) == "1*(x + y)"
+    assert upretty(expr) == "1⋅(x + y)"
+    expr = Mul(x - y, S.One, evaluate=False)
+    assert pretty(expr) == "(x - y)*1"
+    assert upretty(expr) == "(x - y)⋅1"
+    expr = Mul(Rational(1, 2), x - y, S.One, x + y, evaluate=False)
+    assert pretty(expr) == "1/2*(x - y)*1*(x + y)"
+    assert upretty(expr) == "1/2⋅(x - y)⋅1⋅(x + y)"
+    expr = Mul(x + y, Rational(3, 4), S.One, y - z, evaluate=False)
+    assert pretty(expr) == "(x + y)*3/4*1*(y - z)"
+    assert upretty(expr) == "(x + y)⋅3/4⋅1⋅(y - z)"
+    expr = Mul(x + y, Rational(1, 1), Rational(3, 4), Rational(5, 6),evaluate=False)
+    assert pretty(expr) == "(x + y)*1*3/4*5/6"
+    assert upretty(expr) == "(x + y)⋅1⋅3/4⋅5/6"
+    expr = Mul(Rational(3, 4), x + y, S.One, y - z, evaluate=False)
+    assert pretty(expr) == "3/4*(x + y)*1*(y - z)"
+    assert upretty(expr) == "3/4⋅(x + y)⋅1⋅(y - z)"
 
 def test_issue_5524():
     assert pretty(-(-x + 5)*(-x - 2*sqrt(2) + 5) - (-y + 5)*(-y + 5)) == \